Selective breeding of beef sires has been conventionally conducted with a great deal of cost and time. Specifically, the genetic ability of potential sires has been evaluated (progeny test) by selecting bulls and cows based on pedigree information and estimated capabilities, crossing them to produce potential sires, inseminating 7 to 16 cows using the sperm of the potential sires, fattening the resulting calves until they are 21 to 24 months old, and then slaughtering the cattle. However, in spite of such high costs and lengthy time spent for evaluation, cases are often found where potential sires do not possess genetic ability sufficient for the application.
Further, other cases are often found where although fattening farms that fatten and deliver cattle purchase feeder cattle hoping they would produce high-grade beef based on pedigree information, the farms are unable to obtain expected marginal profits, because high-grade beef is not produced.
As described above, useful and available information in addition to pedigree information is required in the field of preliminary selection of sires and selection of feeder cattle.
In the meantime, it has been shown that there is a significant correlation between the growth and texture of beef cattle, and growth hormone levels in blood. Moreover, growth hormone levels in blood are thought to have an effect of promoting the release of accumulated fat from adipose tissue.
The bovine growth hormone gene is composed of 5 exons (portions to be translated into amino acids). Three nucleotide substitutions have been found in the 5th exon, of which two nucleotide substitutions have been shown to be non-conservative substitutions accompanying changes in the amino acid. The non-conservative substitution means that a nucleotide is substituted so as to encode another amino acid differing from the original amino acid. It was reported that a substitution in the vicinity of the 3′ side of the gene of these two nucleotide substitutions contains a genotype, which is currently thought to be present only in Japanese black cattle and Japanese brown cattle (Koichi CHIKUNI et al., Nihon Chikusan Gakkaiho, 65, 340–346, 1994). Furthermore, a method for determining a genotype resulting from a nucleotide mutation in the above bovine growth hormone is known (JP Patent Publication (Kokai) No. 10-136985 A).
However, no effective determination method for selective cattle breeding, for determining the correlation between the genotype of the bovine growth hormone and beef phenotype, has yet been reported.